Process of preparing pigments



Patented Feb. 6, 1934 UNITED STATES PATENT OFFICE PROCESS OF PREPARINGPIGMENTS No Drawing. Original application September 27,

1930, Serial No. 484,937. Divided and this application January 18, 1932.Serial No. 587,453

3 Claims.

This invention relates to improvements in the manufacture of pigments.

Among other features of the invention it is desired to so modify thesurface energy characteristics of ordinary pigments as to give thesepigments greatly improved qualities not hitherto attainable.

The present invention is a division of my copending application SerialNo. 484,937, filed September 27, 1930, and a continuation in part of myapplication Serial No. 399,394, filed October 12, 1929.

The present application distinguishes over Serial No. 399,394 in that itdiscloses coatings of soaps of oxidized fatty acids.

Heretofore the qualities of pigments have de pended largely on thematerials from which the pigments have been made, and on the manner ofmaking them. By the process of the present invention, on the other hand,any kind of pigment, no matter how it has been made, may be treated by aprocess entirely separate from and independent of its own manufacture,whereby its qualities become greatly improved.

Some of the advantages of pigments treated in accordance with thepresent invention are:

1. Better color tone;

2. Greater ease of dispersion;

3. Control of yield value in plastic systems;

4. Better adhesion between pigment and binder or vehicle;

5. Better distribution of particle size;

6. Greater abrasion resistance amt 'tensile strength of their plastics;

7. Smoother and glossier paints and plastics; and

8. Easy removal of moisture.

The surface energy characteristics of pigments play an important part indetermining the properties of the pigment when in contact with a.binding medium. Settling, cohesion, flocculation, gloss, weathering andabrasion resistance are all functions of the surface energycharacteristics. Thus a lead paint on exposure chalks while a zinc oxidepaint fails by cracking largely due to the different surface energycharacteristics of the two pigments.

Pigments may have their surface energy characteristics greatly modifiedby coating their surfaces with-a thin film of certain organic compounds.However it is very necessary that the material used for coating thepigment remain at the pigment binder interface if it is to have thedesired effect. If the material is removed by the binding agent from theinterface as would be an ordinary resin if it were used for coating, itseffect would only be the same as if the same amount of resin wasoriginally dissolved in the oil or binding medium. 01' if the pigmentwere coated with an oil and the oil subsequently oxidized, the adhesionbetween the pigment and the oil in a paint would be very much the sameas if the oil had been added to the pigment in the usual manner. Thatis, the interface would be between oil and pigment whether the pigmentwas added to the oil all at once or if the surface of pigment had beencovered with oil which was then oxidized and the resulting coatedpigment added to the main body of oil to form the paint.

I have found however that the most desirable and permanent modificationof the surface energy characteristics is obtained by causingprecipitated suspensions of water repellent metallic organic compoundsto become adherent upon the surface of the pigment in the form of a thinfilm covering each pigment particle. In the first place, the mostdesirable metallic organic compounds as zinc stearate, calcium oleate oraluminium stearate or resinate are insoluble in water and waterrepellent. And then it does not seem advisable to coat a pigment with awater soluble coating that is permanent since this would greatly destroythe waterproof qualities of the paint film, linoleum or rubber product.In order to reduce the tendency for these metallic compounds to beremoved from the pigment binder interface it is sometimes advisable toprecipitate glue or calcium caseinate in conjunction with them. Thesematerials are rendered insoluble in water to secure their precipitation.The coating material is always of different derivation from the pigmentitself, being formed by a process entirely separate and independent fromthe process of chemical formation of the pigment.

The general procedure in treating pigments by my process is to place thepigment in an aqueous suspension containing a potassium or sodium orother organic water dispersible compound in a quantity equivalent toform a soap 0.2% to 2% of the weight of the pigment introduced. Thissuspension of pigment is well mixed or may be ground in a colloid mill.Then is added the precipitating agent, a metallic salt, in a proportionto cause the precipitation of a suspension of the water repellentmetallic organic compound formed by the reaction of the precipitatingagent on the dissolved or dispersed organic compound.

The proportion of pigment to coating agent depends on the specificsurface of the pigment. The'larger the specific surface the larger isthe amount of coating agent required to cover the surface. Variousfillers and pigments including zinc oxide, whiting, titanium pigment,red slate flour, lithopone and titanium calcium pigment are treated bythe present process.

It-has been found that the soaps of the oxidized fatty acids of thevegetable oils are particularly well adapted for use as coatings forpigment or filler particles. This is because they are much less solublein paint vehicles than soaps made from the usual unoxidized acids. Also,these soaps may be polymerized, or made from polymerized oxidized fattyacids. That is, they may be polymerized either after they are made, orthe oxidized fatty acid may be polymerized and then made into soap.Pigments coated with the soaps made from these oxidized fatty acids willretain their coating indefinitely, while if pigments are coated with thesoaps of the unoxidized fatty acids, this ''-coating is somewhatunstable and liable to be dissolved in the paint vehicle.

The method of applying these soaps as a coating 'to pigments is byprecipitating the soap upon the pigment from an aqueous mediumcontaining the pigment in suspension, and has been set forth in detailin my copending application, Serial No. 399,394, filed October 12, 1929.

An example of the present process is as follows: A pigment is suspendedin water and to the suspension is added a water soluble soap of anoxidized fatty acid such as oxidized linoleic acid. The mixture isagitated or ground in a colloid mill. Then a solution of a zinc saltsuch as zinc sulphate or chloride is added. Other compounds of the typeincluding for instance ferric chloride and barium hydroxide, which willreact with a water soluble soap to form a water insoluble soap may beadded. The water soluble soap and the salt or precipitating agent are soproportioned that the film formed on the pigment is about 0.2% to 2% ofthe weight of the pigment. The resulting material is agitated thoroughlyor ground in a colloid mill. The pigment is allowed to settle, iswashed, filtered and dried according to the usual practice. The pigmenthaving on its surface a thin film comprising a soap of an oxidized fattyacid, is ready for use.

Oxidized fatty acids are prepared by saponifying scrim oil with lye oralcoholic potash and acidifying with hydrochloric acid. The resultantmixture is agitated with petroleum ether. The oxidized fatty acids thencollect as sediment in the petroleumether layer, or adhere to the sidesof the vessel.

The soap formed from scrim oil, which contains generally 50-65% oxidizedfatty acids, will Besides scrim oil made from linseed oil, scrim oil"made from china wood oil, or other drying or semi-drying vegetable oilsmay be used.

Other processes besides the scrim process may be used to secure therequired oxidation of the oil.

It has been found that by using my process of treating pigment surfaceswith Water repellent materials the usual process of freeing the pigmentfrom water by evaporation may be done away -with. In place of thisexpensive evaporation process, pigment which has been treated .by myprocess may be freed from water by simply adding linseed oil to the wetpigment. My process has decreased the afiinity of the pigment for waterand increased the afiinity for oil, so that the oil replaces the water,and the water is forced to the top of the suspension in a clear layer,and is removed by decantation.

What I claim is: i

1. The process of forming an adherent water repellent coating on thesurface of a pigment which comprises dissolving a water soluble soap ofan oxidized fatty acid in an aqueous suspension of a pigment, adding ametallic salt of the type which will react with the water soluble soapto form 'a water insoluble soap whereby the water insoluble soap of anoxidized fatty acid will be precipitated on the suspended pigment andform a coating on the pigment, and removing the pigment from thesuspending medium in the form of individual particles thinly coated withsaid water insoluble soap of an oxidized fatty acid.

2. The process of forming an adherent water repellent coating on thesurface of a pigment which comprises dissolving an alkali metal salt ofoxidized linoleic acid in an aqueous suspension of a pigment, addingzinc sulphate whereby the zinc salt of the oxidized linoleic acid willbe precipitated on the suspended pigment and form a coating on thepigment, and removing the pigment from the suspending medium in the formof individual particles thinly coated with said zinc salt of oxidizedlinoleic acid.

3. A process of preparing pigment material, which process comprisesdissolving a water soluble soap of an oxidized fatty acid in an aqueoussuspension of a pigment, adding a metallic salt of the type which willreact with the water soluble soap to form a water insoluble soap wherebythe water insoluble soap of an oxidized fatty acid is precipitated onthe suspended pigment, the water soluble soap and the said metallic saltbeing so proportioned that a film of the said insoluble soap formed onthe pigment is about 0.2% to 2% of the weight of the pigment, andwashing and drying the resulting pigment material to form individualparticles thinly coated with said water insoluble soap of an oxidizedfatty acid.

JULIAN T. BALDWIN.

CERTIFICATE or CORRECTION.

Patent No. 1,946,054. February 6, 1934.

JULIAN T. BALDWIN.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page 2,after line 92,

insert the following paragraph:

Wherever the term "pigment" appears in the specification and claims, itis meant to include not only pigments as technically considered, butalso all varieties of particles including fillers and other materials ofsimilar nature.

Likewise, wherever the word "film" appears in the specification andclaims,

it is meant to include a group of very small particles of thewater-repellent compound contained or carried on the surface of thepigment.

And that the said Letters Patent should be read with this correctiontherein that the same may conform to the record of the case in thePatent Office.

Signed and sealed this 15th day of May, A. D. 1934.

Bryan M. Battey (Seal) Acting Commissioner of Patents.

